Field of the Invention
The present invention relates generally to a control apparatus, and more particularly to a control apparatus configured to control measuring of an optical property in a test object.
Description of the Related Art
I. M. Vellekoop and A. P. Mosk, “Focusing coherent light through opaque strongly scattering media,” Optics Letters Vol. 32, No. 16 2309-2311 (2007) (simply referred to as “Vellekoop” hereinafter) discloses a technology for irradiating light onto a scattering medium as a test object, such as biological tissues, and for observing scattered light with a CCD which has transmitted through the medium. Vellekoop also discloses a technology for shaping an incident wavefront using a spatial light modulator (“SLM”) so as to improve a light intensity at a specific position in a captured image. Vellekoop demonstrates that the light can be focused on an arbitrary position through the medium after iteration process of measuring the transmitted light intensity and of shaping the incident wavefront. By applying this technology, U.S. Patent Application Publication No. 2013/0182253 discloses a technology using a fluorescent (such as a multiphoton absorption) signal, as a monitoring signal, instead of the transmitted light intensity. U.S. Patent Application Publication No. 2013/0182253 shapes an incident wavefront so as to improve the fluorescent signal, focuses the light on a fluorescent light emitting spot in a medium, and images the fluorescent signal. The technologies of U.S. Patent Applications Publication Nos. 2011/0083509 and 2012/0127557 utilize a focused ultrasound: U.S. Patent Application Publication No. 2011/0083509 uses a photoacoustic signal as a monitoring signal, and U.S. Patent Application Publication No. 2012/0127557 uses ultrasound modulated and frequency-shifted light (ultrasound modulated light) as the monitoring signal. U.S. Patent Applications Publication Nos. 2011/0083509 and 2012/0127557 can focus the light on an ultrasound focus position in the medium by shaping the incident wavefront so as to improve the monitoring signal. Thus, the light can be focused on a position by distance longer than a transport mean free path inside or through the medium by combining the monitoring signal with the wavefront shaping. U.S. Patent Applications Publication Nos. 2011/0083509 and 2012/0127557 can image inside the medium utilizing the monitoring signal with a high signal-to-noise ratio (“SNR”) by improving the intensity of the monitoring signal. C. Ma et al., “Time-reversed adapted-perturbation (TRAP) optical focusing onto dynamic objects inside scattering media,” Nature Photonics, (2014) (simply referred to as “Ma” hereinafter) discloses a technology for focusing light in the medium utilizing displacement of a scatterer or a change of light absorption property in the medium without using a fluorescent probe or a focused ultrasound. Ma records two scattered waves in holograms before and after those intrinsic changes of the medium, and generates a phase conjugate wave based on a wavefront obtained from a difference between these two scattered wavefronts, and again illuminates the medium with the phase conjugate wave. It is demonstrated that the phase conjugate wave propagates to a local position at which the intrinsic change occurs and the inside of the medium can be imaged by utilizing this effect.
In order to focus light in the scattering medium (the test object) utilizing the above wavefront shaping technology, it is necessary to monitor a signal generated from the local position in the test object. When a fluorescent probe is used as the monitoring signal as in U.S. Patent Application Publication No. 2013/0182253, it is necessary to inject the fluorescent probe into the test object and this injection is invasive to the test object. After the injection, it is difficult to arbitrarily change the position of the fluorescent probe, and therefore the light focus position is limited. When the ultrasound is used as in U.S. Patent Applications Publication Nos. 2011/0083509 and 2012/0127557, a ultrasound focus position as well as focus size can be freely controlled from the outside of the test object. However, the apparatus needs an ultrasound system including ultrasound probe, and the ultrasound probe needs to be contacted with the test object and also a matching solution (layer) is necessary between the ultrasound probe and the test object so as to introduce the ultrasound into the test object (acoustic matching). Therefore, in measuring the test object in a noninvasive and noncontact manner, the fluorescence or ultrasound cannot be used as the monitoring signal. On the other hand, a method for utilizing a change of an endogenous optical property in the medium, as in Ma, enables light to be focused in the test object in a noninvasive and noncontact manner and to form an image. Nevertheless, this method which needs generation of the phase conjugate wave, requires the scattered wave emitted from the test object to be recorded in the hologram, where a reference optical path is separately required for the interference measurement. In particular, a transmission type arrangement needs to place detectors in such a manner that the detector can detect object light and reproduced light at both sides of the test object, where object light and reproduced light are passing through the test object in recording and replaying the hologram respectively. As a result, the measurement apparatus becomes relatively complicated. In addition, when an unexpected noise is applied to the endogenous signal before and after the optical property changes, the phase conjugate wave obtained by the difference cannot be correctly focused on the changing spot.